Joint degeneration is the leading chronic condition in the elderly; it affects one in every eight Americans and almost half the population over the age of 65. (Brooks, P. M, Med. J. Aust., 173:307-308, 2000) The most common form of joint degeneration is osteoarthritis. Osteoarthritis weakens and breaks down cartilage and bone, causing pain as bones rub together. Eventually the constant rubbing of the bony surfaces destroys the surfaces that are rubbing against one another leading to rough, painful movement. Total joint replacement, or arthroplasty, represents a significant advance in the treatment of painful and disabling joint pathologies. Arthroplasty can be performed on almost any joint of the body including the hip, knee, ankle, foot, shoulder, elbow, wrist, and fingers. Total joint replacement: whether hip, knee, ankle, foot, shoulder, elbow, wrist, and fingers or other, is typically done as a final stage treatment for a patient who suffers from some form of joint degeneration.
In its early stages, many people manage arthritis pain conservatively by using anti-inflammatory medicines, weight reduction, lifestyle modification, physiotherapy, or occupational therapy. However, as the disease progresses the pain intensifies. When the pain gets to the point where everyday, normal activities such as putting on shoes and socks or walking up stairs become too painful, total joint replacement surgery is an attractive option to restore movement and independence, and to dramatically reduce pain.
Although joint replacement is a relatively large field within orthopedics, the number of fracture fixation devices utilized around the world far outranks the number of artificial joints. Fracture fixation is growing daily as the number of fractures associated with trauma accidents is increasing. Fixation devices can be internal or external in nature and include devices such as a plate, wire, screw, pin, rod, nail or staple, which aid in maintaining fracture fragments in proper position during healing. Such devices are usually inserted after open reduction of the fracture and will remain for the entirety of the healing process, often becoming a permanent structure within the body.
Joint replacement surgery began in the early 1950's, and its frequency has grown as surgical techniques and medical care associated with surgery improves. In the late 1980's between 500,000 and 1 million total hip replacements were performed per year, while in 2004 it is estimated that approximately 600,000 joint prosthesis and 2,000,000 fracture-fixation devices will be inserted into patients in the United States.
Unfortunately, as the number of implant surgeries increases, the number of associated infections also increases. Any person who has an implant is at risk for developing an infection associated with the device. It is estimated that 2 percent of joint prostheses and 5 percent of fixation devices will become infected. Taking 3 percent as an average estimate of infected implants, as many as 30 million incidents of infection may occur.
The effects of implant infection are expensive as well as a danger to the health and well-being of the affected individual. For example, infection results in direct medical and surgical costs and additionally may cause patient pain, suffering, lost wages, lost work and decreased productivity. On average an infected hip prosthesis patient spends six times the number of days in the hospital when compared to the non-infected prosthetic hip patient. In 1991, the total cost of an infected patient, both in hospital and as an outpatient, was $45,000 as compared to the total cost of $8,600 associated with a non-infected patient. (Bengston, S., Ann. Med., 25:523-529, 1993)
Joint replacement implants and fixation devices include a variety of materials foreign to the human body, such as metals, plastics, and polymeric substances, all of which have the potential to serve as substrates for attachment and growth of microorganisms.
In particular, certain microorganisms may exude a glycocalyx layer that protects certain bacteria from phagocytic engulfment by white blood cells in the body. The glycocalyx also enables some bacteria to adhere to environmental surfaces (metals, plastics, root hairs, teeth, etc.), colonize, and resist flushing.
Once microorganisms colonize an implant, it is often very difficult to eradicate or even inhibit the infection. For example, systemic administration of antibiotics is often ineffective due to limited blood supply to the areas of the implant. Additionally, many bacterial species today are resistant to antibiotics.
Where infection cannot be inhibited it may spread and become even more serious, as in patients who have an infection within the bone, osteomyelitis. Such patients often must undergo a difficult and costly treatment involving extended hospitalization, joint debridement, aggressive antimicrobial therapy, total joint removal followed by total joint replacement and possible amputation if the infection can not be eliminated.
Since implantation of an orthopedic implant device, such as a joint replacement prosthesis or fixation device, is quite common and associated infection frequent, there is a continuing need for new approaches to inhibition of infection. In particular, it would be very desirable for both the physician as well as the patient to be able to treat a prosthetic osteomyelitic infection without the removal of an implant. Further, economical and safe apparatus and methods of inhibiting implant associated infections are needed.